Custom Grids

I'm an advanced Atahualpa user who finally caved in, and started messing around with Montezuma.

Awesome theme, but while going through the grid section, the biggest responsive max-size I was able to find was 960px.

Is there a way to get a better use of screen real estate for larger monitors? For example, I would like to use about 1350 px for the content, and still retain the responsiveness of it (kind of like smartpassiveincome.com does - I am modeling my first Montezuma project after that site's layout)

I saw the 100% layout, but I don't necessarily want to go that route either - just looking for something in between

Any tips?